2002-07-08_GENERAL DOCUMENTS - M2002004 (4)

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CombInation with other less suitable soil and spoil materials, must be effectively utilized to provide the best possible postmine land use. Suggested depths of soil replacement are given below. When available, at least 1 foot of topsoil should be respread on all reclaimed soils. When the underlying spoil is coarse - textured (sandy loam or Coarser) and no more than slightly saline (EC <4) or somewhat sodic (SAR <10), from 24 to 30 inches of subsoil which is loam or finer in texture should be applied. If the underlying spoil is silt loam or finer in texture, 12 to 18 inches of subsoil should be respread. If the underlying spoil is moderately sodic (SAR 10 to 20), the subsoil depth should be increas- ed to 24 to 36 inches. When the spoil is sodic (SAR >20), from 36 to 48 inches of subsoil should be applied. If topsoil and subsoil materials are sandy loam or coarser, it is proposed that the suggested depths of subsoil replacement be increased by about 12 inches. These guidelines are summarized in Table 21, and are somewhat higher than the op- timum depths reported in some of the experiments that were cited. However„ until more research data are available describing the changes that occur in unweathered spoil materials placed within the root zone, and until the movement of sodium into replac- ed soil materials from sodic spoil is more fully understood, care must be exercised to ensure that adequate soil materials are replaced to ensure restoration to optimum productive levels. The importance of adequate premine characteriza- tion of soil and overburden materials which iden- tifies the amount and extent of materials with desirable or undesirable strata cannot be over- emphasized. The average properties of the reshaped spoil and the respread soil materials must be deter- mined before mining begins if the depth of soil replacement is to be determined on a site - specific basis. When the overburden has undesirable proper- ties such as coarse texture or high sodium levels, sufficient soil materials must be replaced to ensure optimum production over those sites within the reshaped spoil which have highest levels of these undesirable properties. If, on the other hand, undesirable overburden strata can be selectively placed at a deeper depth during mining, the surface properties of the reshaped spoil may be such that less subsoil will need to be replaced. This has two Important implications. First, if the amount of available soil materials is not sufficient to result in optimum postmine productive levels over undesirable spoil, selective surface placement of good quality spoil could result in higher postmine productive levels. Second, even when sufficient soil materials are available, selective placement of high quality spoil at the surface may justify the replace- ment of Tess subsoil. The decision then becomes an economic consideration in which the cost of selec- tive placement is equated to the savings from decreased removal, stockpiling, and respreading of soil materials. 21 The soil replacement guidelines given above are based upon the results of experiments which have been conducted for a relatively short period. Current evaluations of these results indicate that the initial productive levels can be expected to be maintained or to increase with time, but these experiments need to be monitored for a number of years to confirm this observation. At these sites and at other sites on reclaimed soils, movement of soluble salts and sodium needs to be more precisely described. Changes in physical properties of reclaimed soils such as aggregation, bulk density, and permeability need to be monitored. Research is needed to develop methods for the most effective utilization of marginal soil and spoil materials. As data of these kinds become available, soil replacement guidelines can be further refined. LITERATURE CITED Agricultural Research Service, USDA and North Dakota Ag- ric. Exp. Sta. Staffs. 1975. Progress report on research on reclamation of stripmined lands in the Northern Great Plains. Northern Great Plains Res. and ND Ag. Exp. Stn. Prog. Rpt. 20. Agricultural Research Service, USDA and North Dakota Ag- ric. Exp. Sta. Staffs. 1977. North Dakota progress report on research and reclamation of stripmined lands — Up- date, 1977. 26 p. Agricultural Research Service, SEA/USDA and North Dakota Agric. Exp. Sta. Staffs 1979. Reclamation research supplement to "North Dakota Progress Report on Research on Reclamation of Stripmined Lands — Up- date, 1977." 17 p. Bauer, A. 1980. Responses of tall and semidwarf hard red spring wheat to fertilizer nitrogen rates and water supp- ly in North Dakota. 1974. North Dakota Agric. Exp. Stn. Bull. #510. Bauer, A., G.W. Gee, and J.E. Gilley. 1976. Physical, chem- ical and biological aspects of reclamation of strip -mined lands in western North Dakota. Final Report. Old West Regional Commission, Billings, Montana. 600 p. Carlson, C.W., D.L. Grunes, J. Alessi, and G.A. Reichman. 1961. Corn growth on Gardena surface and subsoil as af- fected by applications of fertilizer and manure. Soil Sci. Soc. Am. Proc. 25:44 -47. Carter, F.S., and E.C. Doll. 1983. Wheat yields on prime and nonprime soils and soil mixtures in a greenhouse study. North Dakota Agric. Exp. Stn., Land Rec. Res. Ctr. Tech. Rpt #3. Dalsted, N.L. and F.L. Leistritz. 1974. North Dakota coal re- sources and development potential. North Dakota Agric. Exp. Stn. Farm Res. 31(6):3 -11. Danielson, R.E. 1967. Root systems in relation to irrigation. In F. M. Hagan, et al. (ed.). Irrigation of Agricultural Lands. Agronomy 11:390 -424. Am. Soc. Agron., Madison, Wisconsin.